Ceramic materials, method of preparing the same and hydrogenation and oxidation processes using the same

ABSTRACT

The present invention relates to ceramic materials containing a homogeneous dispersion of metal particles, particularly sol-gel ceramic materials, a method of preparing the same, and processes for hydrogenating and oxidizing organic compounds using the same.

This invention was made with Government support under Grant No. 2 S07RR07160-14. The Government has certain rights in this invention.

This application is a division of application Ser. No. 498,802, filed onMar. 23, 1990, now U.S. Pat. No. 5,047,354.

BACKGROUND OF THE INVENTION

The present invention relates to ceramic materials containing ahomogeneous dispersion of metal, particularly sol-gel ceramic materials,a method of preparing the same, and processes for hydrogenating andoxidizing organic compounds using the same.

BACKGROUND OF THE INVENTION

Ceramic materials exhibit various technologically important optical,mechanical and electronic properties. As dielectric materials, ceramicshave a wide range of applications including uses in high energy particlebeam accelerators, fusion experiments, free electron lasers and highpowered lasers, high powered X-ray and microwave tubes, electrostaticgenerators, pulse power switches, space platforms, satellites, and solararrays.

Organometallic sol-gel derived optics materials with excellenttransmission properties and low thermal expansion coefficients have beensynthesized Hench, et al. Proc. S.P.I.E.-Int. Soc. Opt. Eng. (1988) 76;Hench, Mater. Res. Soc. Symp. Proc. (1988) 125:189, Hench, N.A.T.O. ASISer., Ser. E. (1985) 92:259. Ultra-low thermal expansion glass has beenproduced from transition metal-containing SiO₂ glasses. Shoup, U.S. Pat.No. 4,786,618.

Metal oxides have been used in the sol-gel process for encapsulation ofmetals in ceramic matrices. Roy et al., Mat. Res. Bull., (1984) 19:169,Roy et al., Mat. Res. Soc. Symp. Proc., (1984) 32:347; Subbanna et al.,Mat. Res. Bull., (1986) 21:1465. The standard method of producingmetal-containing ceramic materials involves 1) dissolution of a metalsalt and Si(OR)₄ in an aqueous/alcoholic solvent at a pH of less than 3or greater than 9 to form a polymer gel; 2) drying of the gel to axerogel, 3) calcination by heating to approximately 500° C. in air, andfinally 4) reduction of the metal salt in hydrogen at 300° C. to 900° C.to produce the metal having a metallic(0) oxidation state.

Trialkylsilanes (R₃ SiH) have been used to reduce transition metal saltsto metals(0) in solution. It is also known in the art thattriethoxysilane decomposes in aqueous solutions to form polysiloxane. Inaddition, the deposition of palladium onto a siloxane polymer has beenachieved by using palladium(II) acetoacetonate and tetraethoxysilanefollowed by calcination. Schubert et al., Chem. Mat., (1989) 1:576.

Thus the conventional approach for incorporation of a metal into aceramic matrix requires harsh (high temperature) reaction conditions.Moreover, reduction of the metal salt occurs only after the calcinationprocess, meaning metal reduction takes place on solid, calcinatedmaterial. Under these conditions uniform reduction of the metal saltcannot be ensured. Nonhomogeneous calcinated products are obtained dueto the fact that entire metal particles remain as cations, or metalparticles are reduced only on their outer surfaces to the metallic(0)state. This stems from the fact that, in general, reactions on solidsare far less efficient than reactions in solution. Moreover, calcinatedceramic materials are difficult to work with in that they cannot beeasily shaped, molded or used to cast thin films.

To overcome these deficiencies of the prior art, applicants sought andfound a method of preparing a ceramic matrix material containing ahomogeneous dispersion of metal particles using sol-gel methods withoutcalcination, in which the metal is completely reduced to the zerooxidation state as it is dispersed in the ceramic matrix material. Inachieving this goal, applicants have also discovered that the resultingsol-gel ceramic matrix material is not only useful for knownapplications of ceramic compositions, but functions as a highly reactiveand selective catalyst for hydrogenation and oxidation reactions. Thisis unusual since, in catalyst development, one normally achieves eithera highly reactive or a highly selective catalyst.

In general, heterogeneous catalysts have been found to be more reactivethan their homogeneous counterparts. Heterogeneous catalysts are oftenmore resilient to air and moisture and they may exhibit longer catalyticlifetimes than homogeneous catalysts. Moreover, heterogeneous catalystscan be removed from a reaction system by simple filtration, and cantherefore be used in flow systems, which makes them particularlyattractive for industrial processes. However, heterogenous catalysts areoften inferior in terms of selectivity. Accordingly, the development ofhomogeneous organometallic complexes for selective hydrogenation hasemerged rapidly over the past two decades. However, the optimum catalystwould yield high selectivity with the advantages of heterogeneoussystems. Applicants have found that finely divided metal encapsulated ina polysiloxane matrix according to the claimed invention is an effectiveand selective catalyst for hydrogenation and oxidation reactions at roomtemperature. The material is both water and air stable.

Silanes have been used in the presence of homogeneous palladiumcatalysts and acid to reduce alkynes, and the reduction of π-allylpalladium species to olefins can be effected using siloxane reagents. Ithas also been reported that platinum(II) complexes are reduced withtriethoxysilane to form platinum(0) colloids and molecular hydrogen.These platinum(0) colloids are active hydrosilylation catalysts.However, the hydrogenated product obtained by these methods containsmetal so finely dispersed that it cannot be removed, even by gelfiltration. Instead, chromatography or distillation must be used toremove the metal from the final product.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a compound comprising apolysiloxane matrix material containing a homogeneous dispersion ofmetal particles, wherein the polysiloxane matrix material isuncalcinated and substantially all of the metal particles are in thezero oxidation state.

The present invention also relates to a method of preparing theuncalcinated polysiloxane matrix material containing a homogeneousdispersion of metal particles in the zero oxidation state, whichcomprises mixing a siloxane compound having Si-H groups with a metalsalt in an aqueous solution; wherein the siloxane compound ispolymerized into a polysiloxane matrix, the metal is reduced to the zerooxidation state, and particles of the metal are homogeneously dispersedwithin the polysiloxane matrix.

The present invention further relates to a process for hydrogenating anorganic compound, which comprises combining a catalytic amount of apolysiloxane matrix material containing a homogeneous dispersion ofmetal particles and the organic compound in the presence of molecularhydrogen, said polysiloxane matrix material being prepared by the methodof mixing a siloxane compound having Si-H groups with an aqueoussolution comprising a metal salt.

The present invention also relates to a process for oxidizing an organiccompound, which comprises combining a catalytic amount of a polysiloxanematrix material containing a homogeneous dispersion of metal particlesand the organic compound in the presence of molecular oxygen, saidpolysiloxane matrix being prepared by the method of mixing a siloxanecompound having Si-H groups with an aqueous solution comprising a metalsalt.

DETAILED DESCRIPTION OF THE INVENTION

Applicants' polysiloxane matrix material containing a homogeneousdispersion of metal particles is unique in that it contains metal in thezero oxidation state while still in the form of a sol, gel or xerogel.This enables the polysiloxane matrix material to be used in a variety ofapplications that require an uncalcinated material, i.e., applicationsthat require molding, coating, and dipping. The polysiloxane matrixmaterial also displays excellent adhesive qualities, most likelygenerated by Coulombic interactions among the metal particles dispersedwithin the matrix.

Suitable metals for encapsulation in the polysiloxane matrix materialinclude those having a standard reduction potential (E°) greater thanthe reduction potentials of H₂ and Si-H. Particularly useful metals arepalladium, rhodium, platinum, ruthenium, copper, silver, antimony,rhenium, iridium, gold, mercury, bismuth, manganese and other metals ofsimilar reduction potentials.

The metal preferably is dispersed within the polysiloxane matrixmaterial in the form of fine particles and in an amount ranging fromabout 0.1 to 15 mole percent. Moreover, the metal is homogeneouslydispersed in the polysiloxane matrix material. Preferably, the particlesize of the metal in the polysiloxane matrix material is less than 100Å, more preferably from 15 to 50 Å.

The compound of the invention may be prepared according to the claimedmethod as follows. A siloxane compound or mixture of siloxane compoundsis combined and reacted with a metal salt in an aqueous solution, i.e.,an aqueous or organic/aqueous solution. The metal salt contains themetal to be dispersed in the polysiloxane matrix.

Suitable siloxane compounds for use in the invention include thosehaving Si-H groups. For example, monoalkoxysilanes, dialkoxysilanes,trialkoxysilanes, and tetralkoxysilanes and mixtures of the same may beused. If tetraalkoxysilanes are used, they must be used in conjunctionwith another siloxane compound. Preferably ethoxysilanes may be used,particularly triethoxysilane and mixtures of triethoxysilane withtetraethoxysilane. The siloxane compound or compounds should be freshlydistilled before use.

On combination in the aqueous solution the siloxane compound polymerizesinto a polysiloxane matrix. The metal salt promotes polymerization. Atthe same time, the metal is reduced to the metallic(0) oxidation stateand is homogeneously dispersed in the polysiloxane matrix. Virtuallyuniform reduction of the metal from a cation to the metallic(0) stateoccurs during this sol-gel process. No heating or calcination steps arerequired, however calcination may be performed subsequently byconventional heating. Alternatively, the polysiloxane matrix materialmay be dried and stored in air for several weeks in the xerogel state.

During reaction of the metal salt and siloxane compound, hydrogen gas isproduced. Both the siloxane and the hydrogen generated in situ serve toreduce the metal from a cationic oxidation state to a metallic(0)oxidation state.

The aqueous solution may comprise water alone or a mixture of water andan organic compound miscible with water and capable of solubilizing thesiloxane compounds used in the method. A useful organic compound istetrahydrofuran (THF). If a mixture of water and THF is used, the volumeratio of THF:water is preferably in the range of 2:1 to 10:1, morepreferably 5:1.

Suitable metal salts for use in the claimed method are those soluble inthe aqueous or organic/aqueous solution and formed from metals having astandard reduction potential (E°) greater than the reduction potentialsof H₂ and Si-H, for example, salts of palladium (II), rhodium (III),platinum (II), ruthenium (II), copper (II), silver (II), antimony (III),rhenium (I), iridium (IV), gold (I), mercury (II), bismuth (III),manganese (III) and the like.

For example, if it is desired to disperse and encapsulate palladium inthe polysiloxane matrix material, suitable metal salts for use in themethod include, for example, palladium(II) acetate and palladium(II)chloride. If it is desired to disperse and encapsulate rhodium in thepolysiloxane material, a suitable metal salt for use in the method is,for example, rhodium(III) chloride.

Applicants' method of preparing the polysiloxane matrix material may becarried out at room temperature, and preferably the reaction is allowedto proceed for at least 2 hours, preferably 4 hours. A more highlycrosslinked matrix may be made with increased reaction time, for example24 hours.

Depending on the siloxane compound and the metal salt used in the abovemethod, various polysiloxane matrix materials can be prepared accordingto this method. For example, reacting triethoxysilane with a metal saltresults in a compound of the formula [OSi(H)O]_(n) --M(0), where Mrepresents the metal. Reacting small amounts of triethoxysilane, largeramounts of tetraethoxysilane and a metal salt produces a compound of theformula (SiO₃)_(n) --M(0). Accordingly, the claimed compound may beprepared wherein it exhibits no Si-H residue.

The polysiloxane matrix material may be isolated from the solution afterreaction by removal of the solvent by drying in vacuo.

In addition to its applications as a sol-gel ceramic material, thepolysiloxane matrix material is an excellent heterogeneous, selectivecatalyst for hydrogenation and oxidation of organic compounds. In thecase of hydrogenation using the claimed compound, the reaction proceedswithout the need for an external hydrogen source, since hydrogen gas isproduced in situ. In addition, applicants believe that suchhydrogenation proceeds by hydrometallic hydrogenation rather thanhydrosilylation followed by protodesilylation.

The hydrogenation process according to the claimed invention comprisesmixing and reacting a siloxane compound, as described above, with anaqueous solution, as described above, of a metal salt, as describedabove, and additionally an organic compound. The siloxane compoundpolymerizes into a polysiloxane matrix while the metal is reduced to themetallic(0) state and is homogeneously dispersed in the polysiloxanematrix material. The organic compound is hydrogenated by thepolysiloxane matrix material and hydrogen. The polysiloxane matrixmaterial may be removed from the reaction solution by filtration.

The oxidation process according to the claimed invention also comprisesmixing and reacting a siloxane compound, as described above, with anaqueous solution, as described above, of a metal salt, as describedabove, and additionally an organic compound. As with hydrogenation thesiloxane compound polymerizes into a polysiloxane matrix, while themetal is reduced to metallic(0) state and homogeneously dispersed in thepolysiloxane matrix. The oxidation reaction is carried out under aninert or O₂ atmosphere. The organic compound is oxidized by thepolysiloxane matrix material and oxygen. Even in an inert atmosphereoxidation proceeds as hydrogen is removed from the organic compound dueto a shift in equilibrium. Again, the polysiloxane matrix material maybe removed by filtration.

The polysiloxane matrix material may be made in advance and stored atroom temperature and pressure, and later used in either thehydrogenation or oxidation process. If prepared in advance, thepolysiloxane matrix material only need be added to the aqueous solutionbefore commencement or hydrogenation or oxidation.

Preferably, hydrogenation or oxidation should be carried out for atleast 30 minutes, preferably 45 minutes, in addition to the timenecessary to form the polysiloxane matrix material. If preparation ofthe polysiloxane matrix material and hydrogenation or oxidation arecarried out at the same time, the reaction should be carried out for atleast 2 hours, preferably 4.5 hours.

The claimed hydrogenation process provides excellent yields of reducedorganic compounds without any significant side products. Hydrogenationof alkynes to alkenes proceeds with very little over-hydrogenation; lessthan about 2 percent of the completely reduced alkane is observed.However, if complete reduction to the alkane is desired, methylpropynoate may be added to the reaction. Preferably 5 to 10 mole percentmethyl propynoate is used in the reaction solution for this purpose. Inaddition, stereoselective hydrogenation may be carried out using theclaimed polysiloxane matrix material.

The following non-limiting examples are designed to further illustratethe claimed invention.

EXAMPLE 1

Dispersion of palladium(0) in polysiloxane using THF/Water (5:1) assolvent. To a solution of palladium(II) acetate (11 mg, 0.05 mmol) inTHF (5 mL, distilled over sodium benzophenone ketyl prior to use) andwater (1 mL deionized water, degassed by passing a stream of argonthrough it for 45 min.) was added freshly distilled triethoxysilane(0.41 g, 0.46 mL, 2.5 mmol) over 5 min. The solution immediately becameblack and rapid hydrogen evolution was observed. The solution wasstirred at room temperature for 4 h. The solvent was removed by rotaryevaporation and the polymer was dried in vacuo for 2.5 days to afford0.14 g of shiny black flakes. Elemental Analysis: C, 1.43%; H, 1.92%;Pd, 0.15%; Si, 41.21%. IR (KBr pellet) 2263.7, 1166.7, 1065, 832.5, 738cm⁻¹. Scanning electron microscopic analysis using energy dispersiveanalysis with X-rays (atomic %): Si, 95.53, 95.61; Pd, 4.47, 4.39.

It is believed that this reaction proceeded as follows: ##STR1##

EXAMPLE 2

Dispersion of palladium(0) in polysiloxane using water as a solvent. Toa solution of palladium(II) acetate (11 mg, 0.05 mmol) in water (5 mL)was added freshly distilled triethoxysilane (0.41 g, 0.46 mL, 2.50 mmol)over 5 min. The solution immediately darkened and rapid hydrogenevolution was observed. The reaction mixture was stirred for 16 h atroom temperature and then filtered. The solvent was removed in vacuo toafford 0.1 g of a gray colored powder. Elemental Analysis: C, 1.89%; H,1.42%; Si, 43.53%; Pd, 0.43%. IR (KBr pellet): 3439, 2255, 1633, 1152,852 cm⁻¹.

It is believed that this reaction proceeded as follows: ##STR2##

EXAMPLE 3

Dispersion of palladium(0) in polysiloxane using a mixture oftriethoxysilane and tetraethoxysilane. Polysiloxane matrix materialcontaining a homogeneous dispersion of palladium(0) particles having noSi-H residue was prepared as follows. To a solution of palladium(II)acetate (0.05 mmol) in water and THF (volume ratio of 1:5) was addedfreshly distilled triethoxysilane (0.25 mmol) along withtetraethoxysilane (2.50 mmol). The solution became black and hydrogenevolution was observed. The solution was stirred for 4 h. The solventwas then removed in vacuo, leaving behind black flakes. FTIR spectrumanalysis showed no absorbance at .sup.˜ 2260 cm⁻¹, indicating that noSi-H residue was left on the polysiloxane matrix material.

EXAMPLE 4

Hydrogenation of 5-decyne to Z-5-decene. To a solution of polysiloxanecontaining a homogeneous dispersion of palladium particles (0.13 g)prepared as described above in THF and water (0.05 mmol Pd), 5-decyne(0.138 g, 0.18 mL, 1.0 mmol) in a solution of THF (5 mL) and water (1mL) was added. Hydrogen was bubbled through the solution for 30 secondsand the reaction was then placed under a hydrogen atmosphere (balloon).The reaction was stirred at room temperature for 4.5 h. Capillary gaschromatograph analysis showed complete consumption of the alkyne and a94% yield of Z-5-decene using dodecane as an internal standard. Theproduct was too volatile for an accurate isolated yield. However, aportion was isolated and analyzed spectroscopically. IR (neat) 2925.5,2850.0, 1460.1 cm⁻¹. ¹ H NMR (300 MHz, CDCl₃)δ 5.33 (br t, J=4.5 Hz,2H), 2.01 (br q, J=5.6 Hz, 4H), 1.3- 1.2 (m, 8H), 0.86 (t, J=6.8 Hz, 6H)[>12:1 Z/E stereochemistry]. ¹³ C NMR (20 MHz, CDCl₃)δ 129.87, 30.25,26.93, 22.25, 13.98.

EXAMPLE 5

Oxidation of 2-methyl-1,4-dihydrobenzoic acid to 2-methylbenzoic acid.To a suspension of 2-methyl-1,4-dihydrobenzoic acid (0.085 g, 0.05 mmol;81% pure, from Aldrich Chemical Company) in decalin (5 mL) under anitrogen atmosphere was added the polysiloxane matrix materialcontaining a homogeneous dispersion of metal particles (0.100 g). Thesolution was heated to reflux for 19 h. On cooling the reaction mixturewas diluted with hexane (25 mL) and extracted with aqueous sodiumhydroxide (5%) solution (2×5 mL). The basic aqueous solution wasacidified and extracted with chloroform (3×4 mL). The combined organiclayer was dried over anhydrous sodium sulfate. Removal of solvent onrotary evaporator gave 2-methylbenzoic acid (0.065 g. 96%). IR(KBr)3600-2000 (br), 2923, 1694, 1300, 920, 731 cm⁻¹. ¹ H NMR (300 MHz,CDCl₃) δ 8.03 (ddd, J=8.5, 3.0, 1.5 Hz, 1 H), 7.42 (td, J= 8.5, 1.5 Hz,1H), 7.26 (td, J=8.5, 1.5 Hz, 1 H), 7.22 (dd, J=8.5, 1.5 Hz, 1 H), 2.64(s, 3 H).

Various examples of the hydrogenation process are shown in Table I.Reactions were allowed to stir for 2-5 hours before filtration of thepolysiloxane matrix material through a plug of silica gel. The reductionproceeded readily on α,β-unsaturated esters and ketones. Excellentchemoselectivity was observed in that while terminal olefinshydrogenated cleanly (entry 12), internal unactivated olefins remainedunreduced (entry 14). The superb stereoselectivity of this process isdemonstrated by entry 17 in the reduction of 5-decyne to Z-5-decene(>15:1 Z:E) in 100% yield, representing a simple alternative to theLindlar reduction process.

The conventional method of stereoselective hydrogenation of unsaturatedhydrocarbons is the Lindlar reduction process. McEwen et al., J. Org.Chem., (1983) 48:4436; Lindlar et al., Org. Synth., (1973) V:880. In theLindlar process, palladium metal deposited on solid BaSO₄ along withquinoline reduces alkynes to cis or Z alkenes. However, in the Lindlarreduction an external source of hydrogen is required, and the amount ofhydrogen gas introduced into the reaction must be monitored carefully,otherwise over reduction to the alkane can occur. Furthermore, syntheticquinoline must be used in the Lindlar process, since commerciallyavailable quinoline normally contains trace amounts of sulfur, which isdifficult to remove and inhibits catalytic activity.

Introduction of methyl propynoate (10 mole %) allowed for the conversionof an internal alkyne to an alkane (entry 17. The complete reactionrequired 24 h). Similarly, both E-5-decene (entry 14) and E-butylhexenoate (entry 6) were unreactive using triethoxysilane alone, butaddition of one equivalent of methyl propynoate to the solution prior tothe addition of triethoxysilane allowed for complete hydrogenation ofthe olefinic moiety. A similar effect was observed in the reduction ofN,N-diethyl cinnamamide (entry 11) in that only partial reductionoccurred in the absence of 10 mole % of methyl propynoate. The reactionrate for hydrogenation of terminal olefins was greatly increased usingmethyl propynoate. The methyl propynoate addition has a profoundinfluence on the course of the reaction, although applicants arepresently not able to rationalize its exact mechanistic action. A morevigorous evolution of hydrogen ensues in the presence of methylpropynoate. Presumably, more active surface sites of the metal areliberated by its addition.

In entries 14, 16 and 17, the capillary gas chromatograph yields weremeasured relative to a dodecane internal standard. The volatility of theproducts prohibited high isolation yields.

Table II lists several other examples of hydrogenation reactionsaccording to the claimed invention using water alone as the aqueoussolution. Again, no external hydrogen source was necessary, and nohydrosilylated material was obtained, meaning hydrogenation proceeds bya true hydrometallic reaction rather than hydrosilylation followed byprotodesilylation. In certain cases, the yield was depressed due tovolatility of the product (entries 3, 4 and 5). In entry 6, a secondportion of triethoxysilane (2.5 equivalents) was added after 1 hour. Inentries 7 (second reaction) and 12, only 1 equivalent of triethoxysilanewas used. In entry 8, several isomeric products were obtained. In entry11, 3 equivalents of sodium hydroxide were added. Propargyl alcohol wasused in certain cases to achieve further hydrogenation, which acts inthe same manner as methyl propynoate. In entries 3 and 8 of Table II,little or no reduction occurred without addition of propargyl alcohol.Entry 7 demonstrates the hydrogenation of alkynes to Z-alkenes with goodselectivity by the addition of one equivalent of triethoxysilane. Allthe products in Table II underwent only standard extractivepurification, yet spectral analysis showed no products other than thoseshown in Table II.

                                      TABLE I                                     __________________________________________________________________________    Hydrogenations Using Triethoxysilane and Catalytic Palladium(II) Acetate      in THF/Water.                                                                 Entry                                                                             Substrate                  Product                    %                   __________________________________________________________________________                                                              Yield                    ##STR3##                                                                                                 ##STR4##                  100                 2                                                                                  ##STR5##                                                                                                 ##STR6##                   96                 3                                                                                  ##STR7##                  No reaction                --                  4                                                                                  ##STR8##                                                                                                 ##STR9##                   91                 5                                                                                  ##STR10##                                                                                                ##STR11##                  92                 6                                                                                  ##STR12##                                                                                                ##STR13##                 --  99              7                                                                                  ##STR14##                                                                                                ##STR15##                 100                 8                                                                                  ##STR16##                                                                                                ##STR17##                  74                 9                                                                                  ##STR18##                                                                                                ##STR19##                  98                 10                                                                                 ##STR20##                                                                                                ##STR21##                  81                 11                                                                                 ##STR22##                                                                                                ##STR23##                 --  90              12                                                                                 ##STR24##                                                                                                ##STR25##                  81                 13  (+)-Longifolene            No reaction                --                  14                                                                                 ##STR26##                 No reaction n-C.sub.10 H.sub.22                                                                          -- 100              15                                                                                 ##STR27##                                                                                                ##STR28##                  94                 16                                                                                 ##STR29##                 n-C.sub.10 H.sub.22         35                 17                                                                                 ##STR30##                                                                                                ##STR31##                 100  90             __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    The reductions of alkenes and alkynes with 5 mole % Pd(OAc).sub.2 and         triethoxysilane in water.                                                     Entry Substrate     Time (h)                                                                           Product                           Yield              __________________________________________________________________________           ##STR32##     4                                                                                  ##STR33##                        93%                2                                                                                    ##STR34##     5                                                                                  ##STR35##                        63%                3                                                                                    ##STR36##     4 5 No Reaction H.sub.11 C.sub.5CO.sub.2 H                                                                           69%               4                                                                                    ##STR37##     4 4                                                                                ##STR38##                                           5                                                                                    ##STR39##      4 14                                                                              ##STR40##                                           6                                                                                    ##STR41##     5   H.sub.11 C.sub.5CO.sub.2 H        78%                7                                                                                    ##STR42##     4 4                                                                                ##STR43##                        92% 99%            8                                                                                    ##STR44##     4 5.5                                                                              C.sub.4 H.sub.9CO.sub.2 H         96%               9                                                                                    ##STR45##     4                                                                                  ##STR46##                        63%                10                                                                                   ##STR47##     5                                                                                  ##STR48##                        81%                11                                                                                   ##STR49##     5                                                                                  ##STR50##                        76%                12                                                                                   ##STR51##     5                                                                                  ##STR52##                        95%                __________________________________________________________________________

We claim:
 1. A process for hydrogenating an organic compound, whichcomprises combining a catalytic amount of a polysiloxane matrix materialcontaining a homogeneous dispersion of metal particles and the organiccompound in the presence of molecular hydrogen, said polysiloxane matrixmaterial being prepared by the method of mixing a siloxane compoundhaving Si-H groups with an aqueous solution comprising a metal salt. 2.The process according to claim 1, wherein 5 to 10 mole percent of anadditive selected from the group consisting of methyl propynoate andpropargyl alcohol is also mixed with the siloxane compound and aqueoussolution.
 3. The process according to claim 1, wherein the siloxanecompound is selected from the group consisting of monoalkoxysilanes,dialkoxysilanes, trialkoxysilanes and mixtures of the same.
 4. Theprocess according to claim 3, wherein the siloxane compound furthercomprises a tetraalkoxysilane.
 5. The process according to claim 1,wherein the siloxane compound is selected from the group consisting ofmonoethoxysilane, diethoxysilane, triethoxysilane, and mixture of thesame.
 6. The process according to claim 5, wherein the siloxane compoundfurther comprises tetraethoxysilane.
 7. The process according to claim1, wherein the metal is selected from the group consisting of palladium,rhodium, platinum, ruthenium, copper, silver, antimony, rhenium,iridium, gold, mercury, bismuth and manganese.
 8. The process accordingto claim 1, wherein the metal salt is selected from the group consistingof palladium(II) acetate and palladium(II) chloride.
 9. The processaccording to claim 1, wherein the metal salt is rhodium(III)trichloride.
 10. The process according to claim 1, wherein the metalparticles have a size of less than 100 Å.
 11. The process according toclaim 1, wherein the metal particles have a size of less than 50 Å. 12.The process according to claim 1, wherein the aqueous solution isselected from the group consisting of water and mixtures of water and anorganic solvent miscible in water and capable of solubilizing thesiloxane compound.
 13. The process according to claim 12, wherein theaqueous solution is a mixture of water and tetrahydrofuran and thevolume ratio of tetrahydrofuran:water is from 2:1 to 10:1.
 14. Theprocess according to claim 12, wherein the aqueous solution is a mixtureof water and tetrahydrofuran and the volume ratio oftetrahydrofuran:water is 5:1.
 15. The process according to claim 1,wherein the polysiloxane matrix contains 0.1 to 15 mole percent ofmetal.